The etiology of cardiovascular disease involves the synthesis and hydrolysis of cholesteryl esters in intestinal, liver and peripheral tissues. These reactions are interfacial and, hence, their rates are determined by the two-dimensional concentrations of reactants and catalysts at the lipid/water interface. Concommitantly, the reactants are distributed among lipid and aqueous bulk phases. The aim of this research is to determine how the structure of interfacial phases regulates the enzyme-catalyzed reaction, CHOLESTERYL ESTER + WATER = CHOLESTEROL + FATTY ACID and the movement of reactants and catalysts to and from the interfacial reaction site. Specifically, we will determine how interfacial structure regulates the rate and extent of adsorption of cholesterol esterases to model interfaces, the rates of cholesteryl ester synthesis and hydrolysis in the interfacial plane and the rates of lipid transport from the lipid-water interface into a bulk lipid or aqueous phase (dissolution) and into another interfacial phase (transbilayer movement). The goal is to relate observed kinetic parameters to the thermodynamic parameters which define interfacial structure. The enzyme dependent processes will be studied using representative cholesterol esterases from pancreatic, lysosomal and cytoplasmic origin to help distinguish enzyme-specific from surface-specific regulation. The reactions will be studied in lipid films at the air/water interface, large unilamellar bilayer vesicles and emulsions. In particular, studies under lipid phase boundary conditions will allow direct comparison of data from the three systems. The results of this study will contribute toward the long term goal of understanding how the interconversion of free and esterified cholesterol is regulated in mammalian tissues and how this contributes to their distribution among biological pools in both normal and pathological states.